Zhanbo Cheng, Xueyu Geng
Biopolymers are gaining attention as sustainable and environmentally friendly soil stabilizers due to their renewability, low carbon footprint, and capacity to enhance soil strength through gelation and interparticle bonding. However, existing studies have predominantly relied on unconfined compressive strength and direct shear tests, providing limited insight into the stress-dependent shear behavior of biopolymer-treated clays under realistic in-situ confinement. This study systematically investigates the unconsolidated undrained triaxial shear behavior of kaolinite clay treated with biopolymers, considering the effects of biopolymer type, concentration, curing condition, and confining pressure. Twelve biopolymers were first evaluated at a dosage of 1% under initial moisture conditions across confining pressures of 100–400 kPa. Five representative biopolymers were further examined at concentrations of 1%–5%, and the influence of curing duration (28, 42, and 70 d) was assessed using 1% xanthan gum-treated specimens under air-drying conditions. The results show that biopolymer treatment markedly enhances peak shear strength and stiffness, with strengthening effects most pronounced at low confining pressures. Cohesion increased substantially, exceeding 110% for sodium alginate, agar, and gellan gum, whereas changes in internal friction angle were moderate and depended on biopolymer type. An optimal biopolymer content of 1%–2% was identified, beyond which marginal or adverse strength gains were observed. Dry curing further promoted shear resistance through dehydration-induced matrix stiffening. A complementary economic assessment indicates that selected biopolymers, particularly xanthan gum, sodium alginate, and agar, can provide mechanically effective and environmentally competitive alternatives to traditional binders for shallow ground improvement.